Harden command redaction for spawn failures

[errfld]

Closes #47

Summary

• replace whitespace splitting with quote-aware command tokenization for redaction
• tighten inline env-assignment detection to valid shell variable names (KEY=value)
• keep executable identification stable for common shell patterns and redact remaining args
• add unit coverage for quoted env assignments, long commands, and non-env commands
• add concise learning note in AGENTS.md

Testing

• cargo test -p git-smee-core executor::tests

Summary by CodeRabbit

• Bug Fixes

  • Enhanced command redaction to reliably detect and redact inline environment variables with quoted values and spaces, ensuring sensitive credentials remain properly hidden in command logs.

• Documentation

  • Added guidelines for secure command handling using quote-aware tokenization and strict environment variable detection.

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📝 Walkthrough

Walkthrough

This PR hardens command redaction in the executor by introducing quote-aware tokenization and environment variable name validation. It replaces simple whitespace splitting with a robust pipeline to prevent inline environment assignment values—including quoted values with spaces—from leaking in spawn error messages.

Changes

Cohort / File(s)	Summary
Documentation AGENTS.md	Adds learning guideline on command redaction emphasizing quote-aware tokenization and strict KEY=value detection for env secret masking.
Command Redaction & Tokenization crates/git-smee-core/src/executor.rs	Introduces tokenize_command() for shell-aware token parsing (respecting quotes and escapes) and is_valid_env_var_name() for env-var validation. Reworks redaction logic to identify the executable via tokenization rather than naive whitespace splitting. Improves inline-env detection using split_once() and name validation. Expands test coverage for quoted env assignments, commands without env prefixes, and truncation behavior.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Possibly related PRs

• refactor(core): model executor spawn failures explicitly #24: Both PRs modify command-redaction and inline-env detection logic in crates/git-smee-core/src/executor.rs, implementing competing or complementary approaches to the same hardening problem.

Poem

🐰 With tokenized care and quotes now aware,
No secrets leak out from the spawn-error snare!
The rabbit hops through each shell-parsed line,
Keeping KEY="value" secrets just fine. ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Harden command redaction for spawn failures' directly and clearly summarizes the main change in the PR, which focuses on hardening the command redaction logic used in spawn error messages.
Linked Issues check	✅ Passed	All acceptance criteria from issue #47 are met: redaction does not leak inline env assignment values, correctly identifies executables with quotes and env vars, and unit tests cover quoted env assignments, long commands, and non-env commands.
Out of Scope Changes check	✅ Passed	All changes are directly related to the hardened command redaction objective: the executor.rs file implements the quote-aware tokenizer and improved env detection, while AGENTS.md adds a learning note explaining the redaction approach.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch codex/gh-47/harden-command-redaction

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